Balloon catheters are widely used in the medical profession for various intraluminal procedures. One common procedure involving the use of a balloon catheter relates to angioplasty dilation of coronary or other arteries suffering from stenosis (i.e., a narrowing of the arterial lumen that restricts blood flow).
Although balloon catheters are used in many other procedures as well, coronary angioplasty using a balloon catheter has drawn particular attention from the medical community because of the growing number of people suffering from heart problems associated with stenosis. As a result, there has been an increase in demand for medical procedures to treat such problems. The widespread frequency of heart problems may be due to a number of societal changes, including the tendency of people to exercise less while eating greater quantities of unhealthy foods, in conjunction with the fact that people generally now have longer life spans than previous generations. Angioplasty procedures have become a popular alternative for treating coronary stenosis because angioplasty procedures are considerably less invasive than other alternatives. For example, stenosis of the coronary arteries has traditionally been treated with bypass surgery. In general, bypass surgery involves splitting the chest bone to open the chest cavity and grafting a replacement vessel onto the heart to bypass the blocked, or stenosed, artery. However, coronary bypass surgery is a very invasive procedure that is risky and requires a long recovery time for the patient.
To address the increase in demand for coronary artery treatments, the medical community has turned to angioplasty procedures, in combination with stenting procedures, to avoid the problems associated with traditional bypass surgery. Typically, angioplasty procedures are performed using a balloon-tipped catheter that may or may not have a stent mounted on the balloon (also referred to as a stented catheter). The physician performs the angioplasty procedure by introducing the balloon catheter into a peripheral artery (commonly one of the leg arteries) and threading the catheter to the narrowed part of the coronary artery to be treated. During this stage, the balloon is uninflated and collapsed onto the shaft of the catheter in order to present a low profile which may be passed through the arterial lumens.
Once the balloon is positioned at the narrowed part of the artery, the balloon is expanded by pumping an inflation solution through the catheter to the balloon. As a result, the balloon presses against the inner wall of the artery for dilation thereof. Typical inflated pressures of the balloon may range between about 6 atm to about 20 atm (i.e., 90 psi-300 psi). If a stent is mounted on the balloon, the balloon inflation also serves to expand, as well as implant, the stent within the artery. After the artery is dilated, the balloon is deflated to collapse onto the shaft of the catheter. The balloon-tipped catheter is then retracted from the body. If a stent were mounted on the balloon of the catheter, the stent would be left permanently implanted in an expanded state at the desired location in the artery to provide a support structure that prevents the artery from collapsing back to its pre-dilated condition. On the other hand, when the balloon catheter is not adapted for delivery of a stent, either a balloon-expandable stent or a self-expandable stent may be implanted in the dilated region in a follow-up procedure. Although the treatment of stenosed coronary arteries is one common example where balloon catheters have been used, this is only one example of how balloon catheters may be used and many other uses are also possible.
Conventional angioplasty techniques can be performed with coaxial balloon catheters. A typical coaxial balloon catheter includes an inner tube and an outer tube coaxially disposed about the inner tube. The inner tube defines a lumen for receiving the guidewire. The area between the inner and outer tubes defines an annular lumen for the passage of inflation fluid. For some applications, a coaxial balloon catheter may be advantageous since its delivery profile may be generally smaller than other kinds of balloon catheters, such as a dual-lumen catheter shaft.
One problem that may be encountered with conventional angioplasty techniques with coaxial balloon catheters is the tendency of the balloon portion to become deformed and wrinkled like an accordion when being inserted into a narrowed site of the body lumen. This tendency can be a result of the amount of axial force forced applied by a physician to situate the balloon portion and distal tip of the inner shaft within the narrowed site, which can cause the inner shaft to move proximally relative to the outer shaft. The amount of relative movement between the shafts can be significant enough to compress or buckle the inner shaft to a degree of permanent deformation. Permanent deformation of the inner shaft can make pushability of the coaxial balloon catheter poorer as the axial force applied at the proximal end will not be sufficiently transferred to the distal end. Further, the ends of the balloon portion can be drawn together sufficiently to deform or wrinkle the balloon portion, which expands the delivery profile of the balloon portion greater than its initial folded state. As a consequence, reintroduction of the coaxial balloon catheters through the introducer sheath and a hemostatic valve that is typically included on the sheath, as well as through other narrowed sites, for additional dilations can become more difficult.